Control of ion energy and angular distributions in dual-frequency capacitively coupled plasmas through power ratios and phase: Consequences on etch profiles

Anisotropic etching, enabled by energetic ion bombardment, is one of the primary roles of plasma–assisted materials processing for microelectronics fabrication. One challenge in plasma etching is being able to control the ion energy-angular distributions (IEADs) from the presheath to the surface of the wafer which is necessary for maintaining the critical dimension of features. Dual frequency capacitive coupled plasmas (DF-CCPs) potentially provide flexible control of IEADs, providing high selectivity while etching different materials and improved uniformity across the wafer. In this paper, the authors present a computational investigation of customizing and controlling IEADs in a DF-CCP resembling those industrially employed with both biases applied to the substrate holding the wafer. The authors found that the ratio of the low-frequency to high-frequency power can be used to control the plasma density, provide extra control for the angular width and energy of the IEADs, and to optimize etch profiles. If the phases between the low frequency and its higher harmonics are changed, the sheath dynamics are modulated, which in turn produces modulation in the ion energy distribution. With these trends, continuously varying the phases between the dual-frequencies can smooth the high frequency modulation in the time averaged IEADs. For validation, results from the simulation are compared with Langmuir probe measurements of ion saturation current densities in a DF-CCP.